1. Technical Field
The present invention generally relates to method and apparatus providing a novel manufacturing process and structure for use with thermal ink jet (TIJ) print heads. More specifically, this invention provides an improved integral print head using an ink heating mechanism comprising a series of resistive, conductive, insulative and ink channel layers defined and deposited on an external orifice plate of a print head.
2. Existing Technology: State of the Art
Methods of fabricating conventional ink jet print heads are known to people skilled in the art of electronic printing. A mechanical printer, like a typewriter, uses moving structures that physically apply ink to paper by striking the paper.
In contrast, an electronic print head converts electrical signals received from a data processing device (such as a computer or calculator) to an output that consists of a readable hard copy such as a sheet of paper or a transparency. Some electronic printers rely upon special treated paper which can be altered by the focused application of heat to form contrasting printed characters. This type of thermal printer is inexpensive, compact, and does not require complex mechanisms that are capable of carefully directing ink to a sheet of paper to form patterns that are read as letters and numerals. Thermal printers that heat portions of the paper to "burn in" readable characters are generally quite limited in their capacity to produce clear, sharp, or finely detailed images.
Another type of thermal printer, called a thermal ink jet (TIJ) printer, uses a supply of liquid ink that is guided to a small constricted region below an orifice and then is rapidly heated to form a bubble which ejects ink through the orifice and which impacts on a piece of paper. Each jet is essentially an orifice aligned with an ink heating apparatus. By carefully selecting and energizing an appropriate combination of jets that are arranged on the face of a print head, letters, numbers, and images can be formed directly on to the paper with great accuracy and precision.
FIG. 1(a) and FIG. 1(b) show schematic views of a state of the art print head.
Print head 10 is shown in cross-section in FIG. 1(a) and in a top view in FIG. 1(b). A conventional ink heating structure 11 includes a substrate 12, an insulative or insulator layer 13, a resistive layer 14 deposited over substrate 12, and two separated sections (of a conductive material layer 16 placed on top of the resistive layer 14. An ink heating zone 18 is located within a gap between portions of the conductive layer 16.
Ink is drawn to heating zone 18 by capillary action and is guided from a remote reservoir 32 by barriers 20. A metal plate 22, formed with a pattern of holes 24, is suspended over heating zone 18. Plate 22 has an outer face 23 which is facing to deliver ink to a face 29 of a printed media such as a sheet of paper 27. When an electrical voltage from an electricity source (not shown) is applied across the gap between the two separated sections 16a and 16b of conductive layer 16, a current flows through resistive layer 14 bridging this gap which defines heating zone 18.
The current quickly heats resistive layer 14, which in turn rapidly raises the temperature of the ink overlying resistor 14. The intense heat creates reproducible vapor bubbles from the superheated ink; the bubbles propel ink through orifices 24 in plate 22. Each orifice 24 in the plate 22 must be carefully aligned with its corresponding heating zone 18.
A typical ink jet print head may include approximately one to fifty holes 24 in orifice plate 22 through which ink droplets are expelled toward a sheet of paper (not shown) that is held directly in front of the print head 10. By simultaneously stimulating many sections of resistive layer 14 across the print head 10, ink is expelled in groups of droplets that form letters, characters, and images once they impact the sheet of paper held in the printer.